| 1. |
- Björnbom, Pehr
(författare)
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Thermodynamic equilibrium of a fluid column under the influence of gravity
- 2021
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Ingår i: Zeitschrift fur Naturforschung A-A Journal of Physical Sciences. - : Walter de Gruyter GmbH. - 0932-0784 .- 1865-7109. ; 76:7, s. 633-652
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Tidskriftsartikel (refereegranskat)abstract
- According to classical and statistical thermodynamics, a well-mixed fluid mass has a uniform temperature andisatthermodynamic equilibrium. It independent of the gravitational field. However, large well-mixed fluid masses, for example, in atmospheres and oceans, often are isentropic. One has attributed that to the influence of gravity. This has raised the question if such masses can go to a different restricted thermodynamic equilibrium with uniform entropy. Discussions on this issue have continued for three centuries without finding a final answer. This paper presents another analysis of the question if a fluid mass under the influence of gravity may go to a restricted equilibrium state with uniform entropy. At first, it analyses previous work as a background study. Then, it describes a kinetic model for the motion of fluid parcels in a vertical fluid column. This model is the tool for studying if and how the column may go to an isentropic equilibrium. The kinetic model supports the hypothesis that a fluid column under the influence of gravity may go to a restricted equilibrium state with an isentropic temperature profile. A statically unstable column can reach that state spontaneously, while its entropy increases and gravitational potential energy decreases. The latter energy is the source of the kinetic energy for the motion of its fluid parcels, driving the internal heat transfer that results in the isentropic profile.
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| 2. |
- Cao, Alec, et al.
(författare)
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Probing Nonexponential Decay in Floquet-Bloch Bands
- 2020
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Ingår i: Zeitschrift fur Naturforschung A-A Journal of Physical Sciences. - : Walter de Gruyter GmbH. - 0932-0784 .- 1865-7109. ; 75:5, s. 443-448
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Tidskriftsartikel (refereegranskat)abstract
- Exponential decay laws describe systems ranging from unstable nuclei to fluorescent molecules, in which the probability of jumping to a lower-energy state in any given time interval is static and history-independent. These decays, involving only a metastable state and fluctuations of the quantum vacuum, are the most fundamental nonequilibrium process and provide a microscopic model for the origins of irreversibility. Despite the fact that the apparently universal exponential decay law has been precisely tested in a variety of physical systems, it is a surprising truth that quantum mechanics requires that spontaneous decay processes have nonexponential time dependence at both very short and very long times. Cold-atom experiments have proven to be powerful probes of fundamental decay processes; in this article, we propose the use of Bose condensates in Floquet-Bloch bands as a probe of long-time nonexponential decay in single isolated emitters. We identify a range of parameters that should enable observation of long-time deviations and experimentally demonstrate a key element of the scheme: tunable decay between quasi-energy bands in a driven optical lattice.
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| 3. |
- Gutman, I., et al.
(författare)
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Estimating and approximating the total pi-electron energy of benzenoid hydrocarbons
- 2000
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Ingår i: Zeitschrift fur Naturforschung A-A Journal of Physical Sciences. - 0932-0784 .- 1865-7109. ; 55:5, s. 507-512
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Tidskriftsartikel (refereegranskat)abstract
- Lower and upper bounds as well as approximate formulas for the total pi-electron energy (E) of benzenoid hydrocarbons are deduced, depending only on the number of carbon atoms (n) and number of carbon-carbon bonds (m). These are better than the several previously known (n, m)-type estimates and approximations for E.
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| 4. |
- Hamzavi, M., et al.
(författare)
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Pseudospin symmetry in the relativistic Killingbeck potential : Quasi-exact solution
- 2012
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Ingår i: Zeitschrift fur Naturforschung A-A Journal of Physical Sciences. - 0932-0784 .- 1865-7109. ; 67:10-11, s. 567-571
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Tidskriftsartikel (refereegranskat)abstract
- The Killingbeck potential consisting of the harmonic oscillator plus Cornell potential, ar2 +br-c/r, is of great interest in particle physics. The solution of the Dirac equation with the Killingbeck potential is studied in the presence of the pseudospin (p-spin) symmetry within the context of quasiexact solutions. Two special cases of the harmonic oscillator and Coulomb potential are also discussed.
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| 5. |
- Hemmingsen, Lars, et al.
(författare)
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Nuclear quadrupole interactions in cadmium complexes : Semiempirical and ab initio calculations
- 1999
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Ingår i: Zeitschrift fur Naturforschung - Section A Journal of Physical Sciences. - : Walter de Gruyter GmbH. - 0932-0784. ; 54:6-7, s. 422-430
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Tidskriftsartikel (refereegranskat)abstract
- Semiempirical calculations, based on the so-called angular overlap model, have been compared with ab initio methods (MP2) for the calculation of nuclear quadrupole interactions (NQI's) in cadmium complexes with biologically relevant ligands (H2O, OH-, cysteinate, carboxylate, and imidazole). The assumptions on which the semiempirical model is based have been tested and the comparison indicates that: 1) A change in the Cd-ligand bond length by 0.1 Å may change the electric field gradient (EFG) by about 0.2 a. u.. A simple scheme to incorporate such effects in the semiempirical method is suggested. 2) The effect of ligand-ligand interactions is up to about 0.2 a. u. for the largest diagonal element of the EFG tensor for the tested complexes, and such effects can significantly influence the so-called asymmetry parameter. 3) The position of non-coordinating atoms on the ligands can in some cases (e. g. the hydrogen atoms of water) significantly influence the EFG. The combined effect of non-coordinating atoms and ligand-ligand interactions may cause deviations of up to 0.35 a. u. between ab initio and the semiempirical calculations. 4) In the semiempirical model each ligand is characterised by one parameter, the so-called partial nuclear quadrupole interaction. This parameter has been evaluated by ab initio calculations, and agreement was found within about 0.2 a. u. (≈ 40 Mrad/s) for all ligands except imidazole. 5) A change in the coordination number from 2 to 6 may change the partial NQI by about 0.3 a. u.
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| 6. |
- Sarwar, Farah, et al.
(författare)
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Linear and Nonlinear Electrical Models of Neurons for Hopfield Neural Network
- 2016
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Ingår i: Zeitschrift fur Naturforschung A-A Journal of Physical Sciences. - : Walter de Gruyter GmbH. - 0932-0784 .- 1865-7109. ; 71:11, s. 995-1002
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Tidskriftsartikel (refereegranskat)abstract
- A novel electrical model of neuron is proposed in this presentation. The suggested neural network model has linear/nonlinear input-output characteristics. This new deterministic model has joint biological properties in excellent agreement with the earlier deterministic neuron model of Hopfield and Tank and to the stochastic neuron model of McCulloch and Pitts. It is an accurate portrayal of differential equation presented by Hopfield and Tank to mimic neurons. Operational amplifiers, resistances, capacitor, and diodes are used to design this system. The presented biological model of neurons remains to be advantageous for simulations. Impulse response is studied and conferred to certify the stability and strength of this innovative model. A simple illustration is mapped to demonstrate the exactness of the intended system. Precisely mapped illustration exhibits 100 % accurate results.
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| 7. |
- Steeb, W-H., et al.
(författare)
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Externally driven nonlinear oscillator, Painlevé test, first integrals and Lie symmetries
- 1993
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Ingår i: Zeitschrift fur Naturforschung A-A Journal of Physical Sciences. - : Walter de Gruyter GmbH. - 0932-0784 .- 1865-7109. ; 48:8-9, s. 943-944
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Tidskriftsartikel (refereegranskat)abstract
- Summary: For arbitrary constants $c\sb 1$, $c\sb 2$ and an arbitrary smooth functions $f$ the driven anharmonic oscillator $d\sp 2 u/dt\sp 2+ c\sb 1 du/dt+ c\sb 2 u+u\sp 3= f(t)$ cannot be solved in closed form. We apply the Painlevé test to obtain the constraint on the constants $c\sb 1$, $c\sb 2$ and the function $f$ for which the equation passes the test. We also give the Lie symmetry vector field and first integrals for this equation.
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| 8. |
- Steeb, Willi-Hans, et al.
(författare)
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Inviscid Burgers equation, Painlevé analysis and a Bäcklund transformation
- 1990
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Ingår i: Zeitschrift fur Naturforschung A-A Journal of Physical Sciences. - : Walter de Gruyter GmbH. - 0932-0784 .- 1865-7109. ; 45:7, s. 929-930
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Tidskriftsartikel (refereegranskat)abstract
- The inviscid Burgers equation is studied with the Painleve analysis. A Bäcklund transformation is constructed. Then we give the symmetry generators. A two-dimensional case is also investigated.
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| 9. |
- Traunmüller, Hartmut, 1944-
(författare)
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Towards a More Well-Founded Cosmology
- 2018
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Ingår i: Zeitschrift fur Naturforschung A-A Journal of Physical Sciences. - : Walter de Gruyter GmbH. - 0932-0784 .- 1865-7109. ; 73:11, s. 1005-1023
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Tidskriftsartikel (refereegranskat)abstract
- First, this paper broaches the definition of science and the epistemic yield of tenets and approaches: phenomenological (descriptive only), well founded (solid first principles, conducive to deep understanding), provisional (falsifiable if universal, verifiable if existential), and imaginary (fictitious entities or processes, conducive to empirically unsupported beliefs). The Big Bang paradigm and the ΛCDM `concordance model' involve such beliefs: the emanation of the universe out of a non-physical stage, cosmic inflation (hardly testable), Λ (fictitious energy), and `exotic' dark matter. They fail in the confidence check that empirical science requires. They also face a problem in delimiting what expands from what does not. In the more well-founded cosmology that emerges, energy is conserved, the universe is persistent (not transient), and the `perfect cosmological principle' holds. Waves and other field perturbations that propagate at c (the escape velocity of the universe) expand exponentially with distance. This results from gravitation. The galaxy web does not expand. Potential Φ varies as -H/(cz) instead of -1/r. Inertial forces reflect gradients present in comoving frames of accelerated bodies (interaction with the rest of the universe - not with space). They are increased where the universe appears blue-shifted and decreased more than proportionately at very low accelerations. A cut-off acceleration a0 = 0.168 cH is deduced. This explains the successful description of galaxy rotation curves by "Modified Newtonian Dynamics". A fully elaborated physical theory is still pending. The recycling of energy via a cosmic ocean filled with photons (the cosmic microwave background), neutrinos and gravitons, and the wider implications for science are briefly discussed.
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| 10. |
- Borchert, G. L., et al.
(författare)
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Mechanisms for K X-Ray-Energy Shifts
- 1987
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Ingår i: Zeitschrift für Naturforschung - Section A Journal of Physical Sciences. - 0932-0784. ; 42:8, s. 781-785
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Tidskriftsartikel (refereegranskat)
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